Hydraulic preheating apparatus for hydraulic oil coolers in a large hydraulic excavator

ABSTRACT

An apparatus for preheating hydraulic oil which is located at low temperatures in at least one air-cooled hydraulic oil cooler, wherein at least one hydraulic oil cooler is arranged outside an engine compartment, in particular of a large hydraulic excavator, characterized in that the oil, in particular hot oil, coming from a tank is fed to the inlet box of the hydraulic oil cooler and is passed on via connecting lines and an interposed pressure relief valve or a non-return valve to the outlet box of at least one hydraulic oil cooler, wherein the outlet box and the cold oil located therein can be heated and fed to the tank.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to international patent application number PCT/EP2011/003823, having a filing date of Jul. 29, 2011, which claims the benefit of priority to German patent application number DE202010011010.6, having a filing date of Aug. 4, 2010, the complete disclosures of which are hereby incorporated by reference for all purposes.

TECHNICAL FIELD

The invention relates to a device for preheating hydraulic oil.

In a large hydraulic excavator, the abovementioned hydraulic oil coolers are normally arranged outside the engine compartment. Owing to said arrangement, when the excavator is used in cold ambient air, the problem arises that, after standstill periods, such as for example upon the initial start-up of the appliance or after repair or servicing work, the hydraulic oil becomes viscous to the point of solidification; this consequently leads to damage in hydraulic oil coolers arranged outside the engine bay and thus to downtime of the large hydraulic excavator.

An air-cooled hydraulic oil cooler is often constructed from fins through which the oil flows, fins through which air passes, and two collecting boxes for the oil flowing in and flowing out.

If a large hydraulic excavator is started up from a standstill at low temperatures, the hydraulic pumps warm up slowly after the starting of the engines. At the same time, the oil in the hydraulic tank, in the lines within the pump chamber and in the main components is heated, wherein the oil in the hydraulic tank is heated to operating temperature quickly. When the oil situated in the hydraulic tank has reached its operating temperature, the temperature sensor mounted in the oil tank activates the fan drive of the hydraulic oil cooler and the cooling oil pump. As a result of the narrow fins in the hydraulic oil cooler and the mounting of the cooler outside the engine bay, the hydraulic oil situated in the oil cooler has not yet undergone any increase in temperature or has not yet undergone a sufficient increase in temperature. As a result of the situation that has now arisen, in which the oil in the hydraulic tank has reached a temperature which necessitates cooling of the oil but the oil situated in the fins of the oil cooler is still cold and cannot be flushed out quickly enough, the back pressure in the system can exceed the burst pressure of the cooler and thus lead to damage to the hydraulic oil cooler.

From experience, the inlet and outlet boxes of the hydraulic oil coolers described further above each have one connector. The oil to be cooled is conducted into the inlet box, from which said oil flows vertically through the fins of the hydraulic oil cooler to the outlet box. The oil flowing into the outlet box is supplied via the outlet connector to the hydraulic tank. Air passes horizontally around the fins of the hydraulic oil cooler during operation.

DE 197 50 814 A1 discloses a heat exchanger, in particular oil cooler, of the type having at least two mutually separate flow ducts for different media, said flow ducts being penetrated by ducts for the inflow and outflow of a medium, and having corresponding connections on said ducts to the ducts for the other medium, and also having a cover which is sealed off in the direction of the heat exchanger and which forms a flow duct and which includes at least one control valve by means of which the temperature-dependent throughflow can be controlled.

DE 699 21 618 T2 presents a cooling and heating system for a machine, for example a wheeled loader or tipper truck, having a main line which is arranged so as to contain a fluid, having a first heat exchanger which is connected to the main line, and having a charge-air cooler for cooling compressed charge air for an internal combustion engine which is arranged in the machine, wherein the charge-air cooler is connected to the main line, wherein a second heat exchanger is connected to the main line downstream of the charge-air cooler, to which second heat exchanger a line for hydraulic liquid is connected such that heat can be transferred between the fluid in the main line and the hydraulic liquid in the line for hydraulic liquid.

SUMMARY

The invention is based on the object of quickly heating solidified hydraulic oil situated in the fins of the hydraulic oil cooler, in particular of a large hydraulic excavator, by means of a bypass flow in order to prevent the abovementioned damage situation.

Said object is achieved in that the in particular hot oil passing from a tank is supplied to the inlet box of the hydraulic oil cooler and is conducted onward via connecting lines and an interposed pressure-limiting valve or a check valve to the outlet box of at least one hydraulic oil cooler, wherein the outlet box and the cold oil situated therein can be heated and supplied to the tank.

If the oil situated in the fins of the oil cooler is still cold, the preheated oil which flows into the inlet box via the first connector and which is at operating pressure is conducted through the inlet box, past the oil cooler fins to the second connector of the inlet box, and onward in the connecting line to the outlet box. A pressure-limiting valve is provided in said line. The pressure port of said valve is connected via the line to the inlet box, and the tank port is connected via a further line to the outlet box of the hydraulic oil cooler.

When the preheated oil which is under pressure now flows via the first connector into the inlet box of the hydraulic oil cooler, a pressure builds up if the oil situated in the fins of the hydraulic oil cooler is cold, because the cold oil cannot immediately be forced out of the fins. Via the second connector of the inlet box, the preheated oil situated in the inlet box is now supplied via the second connector to the pressure-limiting valve. If a preset pressure, which lies below the maximum operating pressure of the hydraulic oil cooler, is exceeded in the pressure-limiting valve, the valve opens and permits the throughflow of oil flowing from the inlet box to the outlet box. As flow passes through the pressure-limiting valve, the oil is heated further and is supplied, according to the invention, to the first connector of the outlet box. The oil is supplied via the second connector from the outlet box to the tank.

The hot oil from the hydraulic tank is thus under pressure at the connector of the inlet box of the hydraulic oil cooler. At the same time, by means of the device described above, hydraulic oil is heated further and is present in the outlet box of the hydraulic cooler. The cooler is thereby heated to such an extent that, with the rising pressure, the still-blocked fins can be flushed out. As a result, the back pressure in the system falls, and the pressure-limiting valve closes. The hydraulic oil cooler then operates in the normal state.

Instead of the pressure-limiting valve, use may also be made of an in particular spring-preloaded check valve.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the invention is illustrated, on the basis of an exemplary embodiment, in the drawing and will be described below. In the drawing:

FIG. 1 shows the present design (prior art);

FIG. 2 is an illustration of the preheating with a pressure-limiting valve;

FIG. 3 is an illustration of the preheating with a spring-preloaded check valve.

DETAILED DESCRIPTION

FIG. 1 shows the prior art in the form of a diagrammatic sketch. By means of a temperature sensor 1, which is arranged in the tank 2, and control electronics 3 (not illustrated in any more detail), hydraulic oil is conducted by means of a delivery pump 4 and via a control valve 5 from the tank 2 into the inlet box 6 of the hydraulic oil cooler 7. The hydraulic oil builds up a pressure in the fins 7′ of the hydraulic oil cooler 7 and forces the cold oil present there into the outlet box 8 of the hydraulic oil cooler 7, from which said oil is conducted via the line 9 to the tank 2.

FIG. 2 shows, in the form of a diagrammatic sketch, the device according to the invention for preheating cold hydraulic oil which is present in the fins 7′ of a hydraulic oil cooler 7. Identical components are denoted by the same reference numerals. It is possible to see the hydraulic oil cooler 7 with the inlet box 6 and outlet box 8, a pressure-limiting valve 13 and the connecting lines 14, 15 from the inlet box 6 to the pressure-limiting valve 13 and from the pressure-limiting valve 13 to the outlet box 8. By means of a temperature sensor 1, which is arranged in the tank 2, and control electronics 3 (not illustrated in any more detail), oil is supplied by means of a delivery pump 4 and via a control valve 5 from the hydraulic tank 2 to the connector 10 of the inlet box 6 of the hydraulic oil cooler 7. When the oil is cold and the pressure set at the pressure-limiting valve 13 is exceeded, the oil present in the inlet box 6 flows via the connector 11 of the inlet box 6 and via the line 14 to the pressure-limiting valve 13, and flows onward from there via the line 15 to the connector 16 of the outlet box 8 of the hydraulic oil cooler 7. The heated oil is supplied via the connector 17 of the outlet box 8 of the hydraulic oil cooler 7 back to the tank 2 via the line 9.

FIG. 3 shows, in the form of a diagrammatic sketch, the device according to the invention for preheating cold hydraulic oil which is present in the fins 7′ of a hydraulic oil cooler 7, wherein in this case, a spring-preloaded check valve 18 is used instead of the pressure-limiting valve 13. The function in this case corresponds to that of FIG. 2. 

1. A device for preheating hydraulic oil in a large hydraulic excavator at low temperatures comprising: at least one hydraulic oil cooler is arranged outside an engine compartment; a tank configured to direct hot oil to an inlet box of the hydraulic oil cooler; connecting lines and an interposed pressure-limiting valve or a check valve configured to conduct the hot oil to the outlet box of the at least one hydraulic oil cooler, wherein the cold oil situated in the outlet box can be heated and supplied to the tank.
 2. The device as claimed in claim 1, wherein the oil flowing from the inlet box of the hydraulic oil cooler to the pressure-limiting valve, or the check valve, and from there to the outlet box of the hydraulic oil cooler is raised from a low temperature level to a higher temperature level before it passes into the outlet box of the hydraulic oil cooler.
 3. The device as claimed in claim 1, wherein the pressure-limiting valve opens the line to the outlet box of the hydraulic oil cooler when a preset response pressure is reached, wherein the preset response pressure lies below the admissible operating pressure of the hydraulic oil cooler.
 4. The device as claimed in claim 3, wherein, when the response pressure preset at the pressure-limiting valve is undershot, the line to the outlet box of the hydraulic oil cooler is closed.
 5. The device as claimed in claim 1, wherein a spring-preloaded check valve can be used instead of the pressure-limiting valve.
 6. A device for preheating hydraulic oil in a large hydraulic excavator, comprising: at least one hydraulic oil cooler having an inlet box and outlet box, and arranged outside an engine compartment and having hydraulic oil at a cold temperature disposed therein; a tank having hydraulic oil at a hot temperature; a pump configured to direct hydraulic oil at the hot temperature to the inlet box a first connecting line having a first end coupled to the inlet box and a second end coupled to a valve; a second connecting line having a first end coupled to the valve and a second end coupled to the outlet box; wherein the first connecting line, the valve, and the second connecting line are configured to conduct hydraulic oil at the hot temperature from the inlet box to the outlet box, so that hydraulic oil at the cold temperature disposed in the outlet box can be heated and returned to the tank.
 7. The device as claimed in claim 6, wherein the hydraulic oil flowing from the inlet box to the valve, and from the valve to the outlet box of the hydraulic oil cooler is raised from a low temperature level to a higher temperature level before passing into the outlet box of the hydraulic oil cooler.
 8. The device as claimed in claim 7, wherein the valve comprises one of a pressure-limiting valve or a check valve, and permits passage of hydraulic oil to the outlet box of the hydraulic oil cooler when a predetermined response pressure is reached, and wherein the predetermined response pressure lies below an admissible operating pressure of the hydraulic oil cooler.
 9. The device as claimed in claim 8, wherein, when a pressure of hydraulic oil in the first line is less than the predetermined response pressure at the valve, the valve is closed.
 10. The device as claimed in claim 9, wherein the valve comprises a spring-preloaded check valve. 